A power source for an implantable medical device, such as a spinal cord stimulator, has a controlledcontoured anterior surface. Preferably, the contoured anterior surface includes a layer of a biocompatible material, such as a polymer. Also preferably, the layer provides a contour generally conforming to the profile of a human buttock. Optionally, a cosmetic implant of generally substantially the same size and shape as the power source is implanted in the opposite buttock as the power source so as to create balance.